Ship Propeller

Definition

A Ship Propeller (often called a "screw") transmits power by converting rotational motion into thrust. A pressure difference is produced between the forward and rear surfaces of the airfoil-shaped blade, and a fluid (water) is accelerated behind the blade.

Types

1. Fixed Pitch Propeller (FPP): The blades are permanently attached to the hub. The pitch is constant. To change speed, the engine RPM changes. To reverse, the engine must stop and restart in reverse.
2. Controllable Pitch Propeller (CPP): The pitch of the blades can be changed mechanically. This allows the engine to run at constant RPM while the ship speed is controlled by changing the blade angle.

Maintenance

Propellers are susceptible to:

• Cavitation: Pitting damage caused by collapsing vapor bubbles.
• Fouling: Marine growth that reduces efficiency (requires polishing).